Fundus camera

ABSTRACT

A hand camera for photographing an eye fundus is provided. The camera consists of a tube ( 3   c ), a camera housing ( 3   a,    3   b ), which camera housing is attached to one end ( 3   d ) of the tube in a light-tight way, a camera device ( 4 ) that is able to record images by means of a two-dimensional optical sensor or a photographical film and that is accommodated in the camera housing ( 3   a,    3   b ), a telephoto lens ( 5 ) that is arranged in the beam path of the light that is reflected from the eye fundus, which is accommodated in the camera housing ( 3   a,    3   b ), a wide-angle lens ( 2 ), which is arranged in the beam path of the light that is reflected from the eye fundus at the other end ( 3   e ) of the tube ( 3   c ), and a light supplying device ( 1 ) consisting of a homogeneous trans-luminescent material, wherein the light supplying device ( 1 ) is arranged with respect to the tube ( 3   c ) in such a way that for a sufficient approach of the other end ( 3   e ) of the tube ( 3   c ) to the eye to be examined the light supplying device touches the sclera of the eye, provided that the center of the wide-angle lens is aligned with the center of the pupil.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a non-provisional application of U.S.Provisional Application Ser. No. 61/295,864, filed on Jan. 18, 2010. Thepresent application also claims priority to German Application No.102010004884.4, filed on Jan. 18, 2010. The entire contents of each ofthese applications are incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention refers to a fundus camera for an imaging of theeye fundus. In particular, the invention refers to a fundus camerahaving compact dimensions, which can be offhand held in the hand.

The basic setup of a fundus camera consists of a multistage opticalsystem, in which a wide-angle lens that is positioned in close proximityto the eye creates an intermediate image, which intermediate image ismapped onto a film or a CCD array by further optical components. Here,the necessity of bringing illumination light into the eye is a problemthat always occurs, when the eye fundus is observed.

Usually the illumination light will enter the eye through the pupil.However, here the problem is met that there are reflexes at therefracting media in the eye, which reflexes interfere with theobservation. U.S. Pat. No. 3,944,341 therefore describes a funduscamera, in which, though the light enters through the pupil, areflection at the lens of the eye is avoided by choosing a ring-shapedillumination by means of optical fibres such that the edge region of thepupil is used for the illumination. In the document two elaboratelydesigned light fibre rings are used for the illumination. However, asthis kind of illumination is elaborate, often the front lens that ispositioned close to the eye is also used for introducing theillumination light, as it is for example described in U.S. Pat. No.3,936,844. Such a design, however, again results in a complex opticaldesign, because the illumination light path and the imaging light pathare close to each other. Thereby, the eye fundus observation device andcamera become very bulky.

Due to the above described problems when using a trans-pupillaryillumination, it was suggested in the prior art such as in U.S. Pat. No.3,954,329 to illuminate the fundus through the sclera. However, thiskind of illumination is rather unusual up to nowadays, though documentU.S. Pat. No. 3,954,329 was already published in 1976. This might berelated to the fact that for a trans-illumination of the sclera theluminous intensity must be high and out of this reason it is notpossible to use a light fibre ring. Hence, in devices of the prior art,in which a trans-scleral illumination is used, usually the light ispunctually radiated through the sclera by means of a fibre bundle (seefor example U.S. Pat. No. 3,943,329). In doing so, it is necessary toradiate through the sclera at more than one position in order tohomogenously illuminate the eye fundus. The necessary installation ofmore than two fibre bundles that results makes the fundus camera bulky.

In view of the above described problems it is an object of the presentinvention to provide a fundus camera that has a compact design, so thatit can be held freely with one hand.

BRIEF SUMMARY OF THE INVENTION

The object is achieved by a hand camera according to claim 1. Furtherimprovements of the invention are described in the dependent claims.

By the invention it becomes possible to build a mobile fundus camerahaving a large angular range of approximately 100° or more. The mobilityof the camera, which can be operated with one hand, saves time andcosts, in particular when patients have to be examined, who are treatedin hospitals outside of the ophthalmological departments. Such a mobilecamera, however, has a remarkable advantage also for premature infants:premature infants are difficult to examine, because they can only betransported cost-intensively and with an increased risk due to theincubator. Thus, a re-location of a premature infant to anophthalmological department, where a stationary fundus camera can beused, turns out to be pretty laboriously. This problem can be solved bythe camera according to the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the following, preferred embodiments of the invention are describedby making reference to the drawings.

FIG. 1 shows a hand camera according to the invention, in which thewide-angle optics has no direct contact to the eye during therecordings, and

FIG. 2 is a hand camera according to the invention, in which thewide-angle optics touches the cornea during the recordings.

DETAILED DESCRIPTION OF THE INVENTION

The camera according to the invention comprises a tube 3 c having awide-angle lens 2 attached to the end 3 e facing the eye to be examined.A telephoto-lens 5 and a camera 4 are attached at the end 3 d of thetube facing away from the eye to be examined. The telephoto-lens 5 andthe camera 4 are surrounded by a housing 3 a, 3 b, which is connected ina light-tight way with the tube 3 c. As can be seen in FIG. 1, theoptics that is used is very simple. Basically the inner space of thetube 3 c is empty. The virtual image that is generated by the wide-anglelens 2 is projected by the telephoto-lens 5 onto a two-dimensionaloptical sensor such as a CCD (charge coupled device) sensor or an APSsensor (active pixel sensor or CMOS sensor) or else onto a photographicfilm.

The camera may be a compact digital camera, which is pretty similar to adigital camera that is offered on the market for private consumers. Thesame applies to the telephoto-lens 5.

In order to change the focus either a commercially available zoom lenscan be used or else a camera housing 3 a, 3 b, as it is represented inFIG. 1, is used. FIG. 1 shows that the camera may be connected to anupper housing part 3 b, which covers a lower camera housing part 3 a,which is connected to the tube 3 c, like a hood. Here, the lower camerahousing part 3 a has the shape of a cylindrical short pipe that is opento the top. When the upper camera housing part 3 b is moved with respectto the lower camera housing part 3 a in a direction of the longitudinalaxis of the tube 3 c, then as a result the distance between thetelephoto-lens 5 and the wide-angle lens 2 can be changed and therebythe focus can be changed. It should be noted that an operator of thecamera can look through a view finder or onto a monitor that is attachedto the backside of the camera in a similar way to commercially availablecameras, wherein neither a view finder nor a monitor are shown in FIG. 1out of simplicity reasons.

In the present invention the eye fundus is illuminatedtrans-sclerically. For this purpose a cylindrical ring attachment 1 outof a trans-luminescent material is attached to the end 3 e of the tube 3c that is facing the eye. This ring attachment, which serves as a lightsupplying device, is put onto the eye concentrically to the cornea closeto the limbus, so that the attachment rests on the eye on the scleraoutside of the pupil. Light can be supplied to the ring attachment 1from a light source 6. This may be effected for example by means ofoptical fibres that are coupled to the sidewall of the ring attachment1. For example, a short pipe out of the trans-luminescent material ofthe ring attachment 1 may protrude from the sidewall of the ringattachment 1. Then an appropriate coupling device for attaching orscrewing a cable that contains the light-conducting fibres is affixed onthis short pipe.

As the eye has a curvature and as the ring attachment 1 rests on the eyewith its face side on the eye, it is advantageous to have a surface areaof the face side, which does not form a right angle with thelongitudinal axis of the tube 3 c. For example, the outer edge of thering may further protrude towards the eye than the inner edge. Ideally,the face surface of the ring attachment additionally has a curvature,which curvature is adapted to the curvature of an average eye.

For the light guidance the ring attachment utilizes a total reflectionof the light at the interface between the ring material and thesurrounding air. Thus, the light is shone uniformly through the ringattachment and ideally is shone annularly through the sclera.

The ring attachment 1 may be made from a trans-luminescent plasticmaterial or from glass. By using such a ring attachment, which is madefrom a homogenous material, a higher luminous intensity is obtainedcompared to a light fibre ring. Among other things this is due to thefact that the light fibres have a total area that is much smaller thanthe total area of the ring attachment. While light-guiding fibresusually have a diameter of a few 100 μm, the wall thickness of the ringattachment may be a few mm. Furthermore, by the selection of aparticular ring material losses in the light conduction can beminimized.

Compared to the use of light-guiding fibres there is still a furtheradvantage when using such a ring attachment:

Light-guiding fibres are known to heat up very much due to the heatconduction of the material. This may lead to a damage of the cells ofthe connective tissue in the eye, onto which the light-guiding fibres ofthe prior art are put when the temperature exceeds 42° C. In theinvention such a heating-up is avoided already due to the larger contactsurface at the eye. Moreover, by a selective choice of the material, atoo excessive heating-up of the face surfaces of the ring attachmentthat are resting on the eye can be avoided. For example, borosilicateglass 3.3 may be used as ring material, which material blocks short-waveand long-wave portions of the radiation. In order to avoid damages, itis in any case advantageous to choose a diameter of the ring attachment1 such that the ring attachment 1 rests on a position of the sclera thatcontains as few blood vessels as possible, when the pipe 3 c iscentrical to the pupil. For example, the diameter of the ring attachmentmight be chosen such that the distance between the position at which thering attachment rests on the sclera and the limbus is approximately 2mm.

By the fundus camera according to the invention a mobile hand camera isprovided. In particular, such a camera might be held by the operator inhis hand during the examination without the need of having to use acamera tripod. Ideally, the use of the camera is not much morecomplicated than the use of an ordinary digital camera. A red cast ofthe pictures that usually appears in a trans-scleral illumination can becomputationally eliminated by the camera software after adigitalization. Thereby, complicated optics or various colour filters inthe illumination light path in order to correct the colour are avoided.

The trans-scleral illumination has the decisive advantage that there areno problems with reflections at the lens of the eye. Furthermore, it isalso a decisive advantage that examinations are possible even for smallpupil diameters or pathological changes of the lens that make atrans-pupillar illumination impossible. For example, the formation oftumors may make impossible an illumination through the edge region ofthe pupil. As was already mentioned in the beginning, the camera isparticularly suitable for an examination of premature infants. In orderto make this possible, simply a ring attachment 1 having a smallerdiameter and a steeper radius than the diameter and radius that areprovided for adults have to be selected. “Steeper radius” here means thefollowing: due to the larger curvature of the small eye of the prematureinfant the face surface of the ring attachment is formed such that theouter edge of the ring protrudes towards the eye to a larger extent thanin the case of the ring attachment for adults.

Finally, the trans-scleral illumination makes it possible to illuminatethe whole fundus, which is not possible in that way for a trans-pupillarillumination due to the limited diameter of the pupil. As a result, fora corresponding selection of the wide-angle lens 2 field viewing anglesup to 165° are possible. In conjunction with FIG. 1 a ring attachment 1was described that completely surrounds the pupil. The reason for such acomplete surrounding of the pupil is a supply of the illumination lightthat is as uniform as possible. Of course the illumination light canalso be trans-illuminated through the sclera at several positions aroundthe pupil that are separated from each other. For example, the facesurface of the ring attachment that is put onto the eye, may haverecesses. In an extreme case these recesses may even take up most of thewall surface of the ring attachment. Thereby, the ring attachment 1 canrest on the sclera e.g. at six, five, four, three or even only twopositions. Of course, the positions at which the ring attachment 1touches the sclera preferably should have the same distance to eachother in a circumferential direction around the pupil.

Of course, it is also possible to use a lens system or an optics havingfurther elements instead of a wide-angle lens 2. However, the simplersuch a wide-angle optics 2 and the fewer components it has, the smalleris the weight of the hand camera. The term “wide-angle optics” hereshall comprise also optics that consist only of a singular wide-anglelens.

The wide-angle optics 2 that is arranged at the end 3 e of the tube 3 cthat is facing the eye, may be arranged with respect to the face surfaceof the ring attachment 1 that shall be put onto the eye in such a way,that the wide-angle optics 2 is put onto the cornea of the eyesimultaneously with the ring attachment hitting the sclera (indirectophthalmoscopy, see FIG. 2). However, the wide-angle optics can also bearranged in the tube 3 c such that it has a certain distance to the end3 e of the tube 3 c that is facing the eye (see FIG. 1). In an idealcase the wide-angle optics 2 can be moved along the longitudinal axis ofthe tube 3 c.

In a further embodiment of the invention there is no ring attachment 1and the illumination light is supplied via a rod made of atrans-luminescent homogeneous material, wherein the rod is put onto apart of the sclera. Due to the high luminous intensity resulting fromthe use of such a light rod, provision can be made for a sufficientillumination of the eye fundus, though the sclera is trans-illuminatedonly at one point. Furthermore, the light rod may consist of the samematerials as the ring attachment 1. The ring attachment 1 as well as thelight rod may be covered by a light-reflecting material such as a silverlayer or a metal pipe in order to improve the light-conducting ability.

According to a variant of the invention the light rod or the ringattachment can be moved independently from the tube 3 c. In such a caseonly the light rod or the ring attachment are put onto the eye while thetube 3 c with the wide-angle optics is held at a certain distance to theeye. Here, a mounting of the camera to a cross slide may beadvantageous, because one hand is needed for the positioning of thelight rod or the ring attachment.

In general it is advantageous, if the hand camera can also be mounted ona cross slide. When the cross slide is mounted at a height-adjustabletable, a stationary unit is obtained, when the hand camera is fixed atthe cross-slide. With such a stationary unit photos or movies at asitting patient can be made. For example, for tumor patients it isimportant that the recordings are made at a sitting patient as well asat a lying patient. The recordings in a lying condition then are madewith the hand camera, which is not mounted at a cross-slide.Furthermore, it is possible to connect the camera to a monitor via acable, so that it is possible to view the camera picture on the monitor.

It is finally noted that the use of the term “cylinder” in the presentapplication is not limited to a circular cylinder. Rather, the term“cylinder” is used in a mathematical sense and generally includes bodiesthat are limited by two parallel plane surfaces having an arbitraryshape and by a lateral surface that is connecting these surfaces.However, in particular this term shall designate any straight cylinder,in which the lateral surface is perpendicular to the bottom surface andthe top surface.

1. A hand camera for photographing an eye fundus comprising: a tube, acamera housing, that is attached in a light-tight way at one end of thetube, a camera device, that is able to record images by means of atwo-dimensional optical sensor or a photographic film and that isaccommodated in the camera housing, a telephoto lens arranged in a beampath of light that is reflected by the eye fundus, the telephoto lensbeing accommodated in the camera housing, a wide-angle optics that isarranged in the beam path of the light that is reflected from the eyefundus at the other end of the tube, and a light supplying device, whichconsists of a homogeneous trans-luminescent material, wherein the lightsupplying device is able to be put onto the sclera of the eye to beexamined for a trans-scleral illumination of the eye fundus.
 2. The handcamera according to claim 1, wherein the light supplying device isarranged with respect to the tube in such a way, that the lightsupplying device touches the sclera of the eye when the other end of thetube is sufficiently approached to the eye to be examined, provided thatthe centre of the wide-angle optics is aligned with the centre of thepupil.
 3. The hand camera according to claim 1, in which the lightsupplying device is a light rod.
 4. The hand camera according to claim1, in which the light supplying device is a ring attachment shaped likea hollow cylinder, the ring attachment being attached to the other endof the tube such that the ring attachment can be put onto the sclera ofthe eye with a face surface being concentric to the pupil.
 5. The handcamera according to claim 4, in which the ring attachment has at leastone recess at the face surface, which face surface is to be put onto thesclera, wherein the recess is formed such that the face surface consistsof a plurality of partial surfaces.
 6. The hand camera according toclaim 5, in which the at least one recess of the face surface is formedin such a way that the face surface consists of a plurality ofindividual partial surfaces, which have a distance to each other.
 7. Thehand camera according to claim 1, in which the homogeneoustrans-luminescent material consists of glass or a plastic.
 8. The handcamera according to claim 7, in which the homogeneous, trans-luminescentmaterial is a borosilicate glass 3.3.
 9. The hand camera according toclaim 1, in which the light supplying device is covered by a layer thatis reflecting to the inside of the light conducting device.
 10. The handcamera according to claim 1, in which the wide-angle optics is arrangedin such a way that when the light supplying device is put onto thesclera, the wide-angle optics touches the cornea of the eye when thelight supplying device touches the sclera.
 11. The hand camera accordingto claim 1, in which the wide-angle optics is arranged inside of thetube and in which the position of the wide-angle optics in the tube canbe varied along the longitudinal axis of the tube.